The invention relates to devices for detecting bio-molecules and/or bio-molecules interactions and methods of making the same, and more particularly to such detection devices having in-line desalting and methods of making the same.
Proteomics offers great potential for discovering biomarker patterns for earlier screening and detection of lethal and infectious diseases, systematic monitoring of physiological responses to drugs, and selecting the best treatment options for individual patients. For routine clinical use, an inexpensive, easy-to-use, multiplexed and high throughput protein analysis platform is needed, with high sensitivity and specificity for detection of low-abundance biomarkers in serum or other body fluids. There is also a need for high throughput and highly integrated sensor arrays for drug screening.
Nanostructured sensor arrays that use purely electrical detection, such as a field effect transistor (FET), fabricated with Si or other semiconductors, offer some of the desired characteristics. In such a device, a device channel of Si or other semiconductors is defined between two electrodes. The surface of the semiconductor channel or its oxide surface may be modified and covalently functionalized with antibodies or other receptor ligands for quantitative biorecognition. The binding of protein or other biomolecules induces net charge change, or change in dipole moment and binding-induced dipoles or modification of energy distribution and/or density of surface states. These binding events can change surface potential of the FET device and therefore modulate the conductance of the semiconductor channel. A small voltage or current, small enough not to disturb biomolecule interactions, is applied between two electrodes, and the change in conductance of the device channel is related and calibrated to the analyte concentration in a solution. When the device channel is reduced to nanoscale, the detection limit can be significantly reduced due to increased surface-to-volume ratio. Further, the response time can also be reduced due to favorable mass transport at low analyte concentrations due to small binding capacity of the small sensing surface. The ultra low detection limit of the nano-FET sensor at low ionic strength solutions has been recently demonstrated.
However, these devices may be rendered ineffective due to the screening effect in higher ionic strength solutions. The Debye screening length is defined as the distance from the sensing surface where potential change can be detected by the sensing device. In a high ionic strength solution, the screening length is reduced by ions and thus, binding events occurring beyond the screening length cannot be detected. It has been shown that it is required to desalt the sample to sensitively detect the antigen since the physiological salt concentration can overwhelm the change in local charge brought about by the binding of the antigen to the antibody. This arises because at physiological concentrations of salt (˜200 mM), the debye shielding layer is reduced to ˜1 nm. An antibody molecule is approximately 10 nm in size, therefore the binding event is outside the debye layer thickness.
Samples can be desalted offline by repeated concentration and dilution on an ultrafiltration membrane in a centrifuge tube designed for this purpose. Alternatively, dialysis can be used, however, the process is slow. Samples can also be desalted in gel filtration columns but low molecular weight species can be lost with the salts and the process dilutes the sample, which is undesirable for high sensitivity analysis.
It would be desirable to provide a method and a device that would enable in-line/on-chip desalting for nano-FET biosensor while avoiding the need to desalt the sample offline since this step complicates the implementation of such a detector in a variety of applications (e.g. point-of-care).